Highly-integrated, low-cost circuits have fueled the growth of BiCMOS technology for Radio-Frequency (“RF”) applications. Aggressive technology scaling and the integration of bandgap-engineered Silicon-Germanium (“SiGe”) technologies have resulted in dramatic performance improvements of silicon-based RF integrated circuits, thus providing cost advantages over III-V technologies. RF switches are crucial for operation of any radar or wireless transceiver. In addition to transmit/receive functionality, RF switches can be used for digital gain control and phase state selection in a typical RF frontend.
Several specifications can be used to measure the performance of an RF switch, including insertion loss, compression point, single event effect immunity, isolation, and linearity. Insertion loss refers to signal loss that occurs when an RF switch is placed between a transceiver and an antenna. Thus, a goal of RF switches is to minimize insertion loss. An RF switch's compression point refers to the maximum power handling capability of the switch. Thus, a goal of RF switches is to maximize the compression point. Single event effect immunity refers to a switch's immunity to resist strikes from heavy ions, which can cause transistors to be shorted together. Thus, a goal of RF switches is to maximize the single event effect immunity. Isolation refers to signal leakage from the transmitter to the receiver when the transmitter is transmitting a signal, and vice versa. Thus, a goal of RF switches is to maximize isolation, which minimizes signal leakage. Finally, linearity refers to a switch's ability to maintain the amplitude and phase information in a modulated signal and limit or prevent intermodulation distortion as the frequency of the signal is increased. Thus, a goal of RF switches is to maximize linearity.
Conventional RF switches operate by switching the base-emitter junction of a bipolar transistor. This type of switching is known as forward-mode switching. Unfortunately, conventional RF switches have been unable to realize the benefits of SiGe Heterojunction Bipolar Transistors (“HBTs”). Due to the higher non-linearity in conventional SiGe HBTs, conventional RF switches in systems with high linearity or dynamic range requirements have been forced to employ CMOS-based RF switches. While technology scaling and layout optimization has resulted in low insertion loss for CMOS-based RF switches, shorter channel length and a thinner oxide has limited the dynamic range and high power handling capability of the CMOS switches. Recently, near one watt X-band Power Amplifiers (“PA”) in SiGe BiCMOS technology have been demonstrated. Further, SiGe HBT device performance has been constantly improving, such that fT is now routinely above 200 GHz—even approaching 500 GHz. Therefore, there is a need for high power handling silicon RF switches. Because solutions already are available for integrating the balun and high power PA on a single chip, a high power, low insertion loss, and high linearity T/R RF switch becomes the last external component (excluding the crystal oscillator) that needs to be integrated on a chip to provide the most cost-efficient system-level solution. The present invention is primarily directed to such an RF switch.